Uptake of extracellular enzyme by a novel pathway is a major determinant of cathepsin L levels in human macrophages.

Abstract

The phorbol myristate acetate (PMA)-differentiated myelomonocytic cell line, THP-1, and human alveolar macrophages contain the cysteine proteinase cathepsin L. This enzyme is synthesized as a 43-kD proenzyme and processed to the active 25-kD form. Differentiation of THP-1 cells in the presence of human serum resulted in a increase in the size of the vacuolar compartment and the accumulation of more 25-kD cathepsin L antigen, as compared with THP-1 cells differentiated in the presence of fetal calf serum. Cells cultured in both types of sera have equivalent levels of cathepsin L mRNA. Metabolic labeling experiments demonstrated equivalent rates of synthesis, processing to the active form, and persistence in both culture conditions. An extracellular source of enzyme was documented by immunoblotting human serum which demonstrated 25-kD cathepsin L antigen; furthermore, we demonstrated that both THP-1 cells, differentiated in human serum, and human alveolar macrophages take up the 43-kD proenzyme and process it to the 25-kD form. Thus, human serum contains a factor(s) that induces both a marked increase in the size of the vacuolar compartment in differentiated THP-1 cells and a novel pathway that is responsible for the uptake and processing of extracellular cathepsin L. The activity of this inducible pathway is a major determinant of levels of intracellular cathepsin L. Cathepsin L is a potent elastase and the regulation of its uptake and processing may play a role in the pathogenesis of disease processes characterized by the destruction of elastin, such as pulmonary emphysema. (J. Clin. Invest. 1990. 86:176-183.)

Metalloelastase is required for macrophage-mediated proteolysis and matrix invasion in mice.

“…Note the doublet at 20-22 kDa characteristic of metalloelastase (3,4) (16). While several purified macrophage proteinases have the capacity to solubilize elastin (3,(17)(18)(19)(20), the precise role of each of these proteinases in the context of the intact cell is unclear. To assess the relative contribution of MME to macrophage-mediated elastolysis, macrophages were cultured on [3H]elastin at pH 7.4.…”

Alveolar macrophage-mediated elastolysis: roles of matrix metalloproteinases, cysteine, and serine proteases

“…Similarly, the finding of significant levels of cysteine protease activity in pure macrophage culture can be partially explained by uptake of neutrophil-derived cathepsin L (36,40). However, macrophages can manufacture both cathepsin L and cathepsin S after stimulation (41,42).…”

“…Semiquantitative measurement of MMP activity was performed by zymography (26,36). Briefly, samples (15 l) and standards (1 g; Amersham Pharmacia Biotech, Little Chalfont, UK) were loaded into 10% polyacrylamide gels (wt/vol) incorporating 0.1% (wt/vol) gelatin substrate.…”

Proteolytic Processing of Cut Homeobox 1 by Neutrophil Elastase in the MV4;11 Myeloid Leukemia Cell Line

“…4D, fourth panel). Indeed, PMA was previously shown to induce cathepsin L expression in various cell lines (30,31). In summary, results from expression analysis revealed that neutrophil elastase was the only serine protease whose expression was both elevated in MV4;11 cells and reduced upon treatment of cells with PMA.…”